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diff --git a/hsm-gpio/Hsm/GPIO/FFI.hsc b/hsm-gpio/Hsm/GPIO/FFI.hsc
new file mode 100644
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+++ b/hsm-gpio/Hsm/GPIO/FFI.hsc
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+{-# LANGUAGE CApiFFI #-}
+
+-- FFI bindings to `libgpiod` for direct GPIO hardware access.
+--
+-- Exposes only the minimal required subset of `libgpiod` functionality used by
+-- this project. The bindings are suitable for low-level hardware control.
+--
+-- Future work could expand this into a comprehensive `gpiod` binding package.
+module Hsm.GPIO.FFI
+  ( chipOpen
+  , chipClose
+  , input
+  , output
+  , LineValue
+  , active
+  , inactive
+  , lineSettingsNew
+  , lineSettingsFree
+  , lineSettingsSetDirection
+  , lineSettingsSetOutputValue
+  , lineConfigNew
+  , lineConfigFree
+  , lineConfigAddLineSettings
+  , requestConfigNew
+  , requestConfigFree
+  , requestConfigSetConsumer
+  , LineRequest
+  , chipRequestLines
+  , lineRequestRelease
+  , lineRequestSetValue
+  , lineRequestSetValues
+  )
+where
+
+import Foreign.C.String (CString)
+import Foreign.C.Types (CInt (CInt), CSize (CSize), CUInt (CUInt))
+import Foreign.Ptr (Ptr)
+import Foreign.Storable (Storable)
+
+data Chip
+
+foreign import capi unsafe "gpiod.h gpiod_chip_open"
+  chipOpen :: CString -> IO (Ptr Chip)
+
+foreign import capi unsafe "gpiod.h gpiod_chip_close"
+  chipClose :: Ptr Chip -> IO ()
+
+data LineSettings
+
+newtype LineDirection
+  = LineDirection CInt
+  deriving Show
+
+foreign import capi "gpiod.h value GPIOD_LINE_DIRECTION_INPUT"
+  input :: LineDirection
+
+foreign import capi "gpiod.h value GPIOD_LINE_DIRECTION_OUTPUT"
+  output :: LineDirection
+
+newtype LineValue
+  = LineValue CInt
+  deriving (Show, Storable)
+
+foreign import capi "gpiod.h value GPIOD_LINE_VALUE_ACTIVE"
+  active :: LineValue
+
+foreign import capi "gpiod.h value GPIOD_LINE_VALUE_INACTIVE"
+  inactive :: LineValue
+
+foreign import capi unsafe "gpiod.h gpiod_line_settings_new"
+  lineSettingsNew :: IO (Ptr LineSettings)
+
+foreign import capi unsafe "gpiod.h gpiod_line_settings_free"
+  lineSettingsFree :: Ptr LineSettings -> IO ()
+
+foreign import capi unsafe "gpiod.h gpiod_line_settings_set_direction"
+  lineSettingsSetDirection :: Ptr LineSettings -> LineDirection -> IO CInt
+
+foreign import capi unsafe "gpiod.h gpiod_line_settings_set_output_value"
+  lineSettingsSetOutputValue :: Ptr LineSettings -> LineValue -> IO CInt
+
+data LineConfig
+
+foreign import capi unsafe "gpiod.h gpiod_line_config_new"
+  lineConfigNew :: IO (Ptr LineConfig)
+
+foreign import capi unsafe "gpiod.h gpiod_line_config_free"
+  lineConfigFree :: Ptr LineConfig -> IO ()
+
+foreign import capi unsafe "gpiod.h gpiod_line_config_add_line_settings"
+  lineConfigAddLineSettings :: Ptr LineConfig -> Ptr CUInt -> CSize -> Ptr LineSettings -> IO CInt
+
+data RequestConfig
+
+foreign import capi unsafe "gpiod.h gpiod_request_config_new"
+  requestConfigNew :: IO (Ptr RequestConfig)
+
+foreign import capi unsafe "gpiod.h gpiod_request_config_free"
+  requestConfigFree :: Ptr RequestConfig -> IO ()
+
+foreign import capi unsafe "gpiod.h gpiod_request_config_set_consumer"
+  requestConfigSetConsumer :: Ptr RequestConfig -> CString -> IO ()
+
+data LineRequest
+
+foreign import capi unsafe "gpiod.h gpiod_chip_request_lines"
+  chipRequestLines :: Ptr Chip -> Ptr RequestConfig -> Ptr LineConfig -> IO (Ptr LineRequest)
+
+foreign import capi unsafe "gpiod.h gpiod_line_request_release"
+  lineRequestRelease :: Ptr LineRequest -> IO ()
+
+foreign import capi unsafe "gpiod.h gpiod_line_request_set_value"
+  lineRequestSetValue :: Ptr LineRequest -> CUInt -> LineValue -> IO CInt
+
+foreign import capi unsafe "gpiod.h gpiod_line_request_set_values"
+  lineRequestSetValues :: Ptr LineRequest -> Ptr LineValue -> IO CInt